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354                   HEAVY OILS  (LUBRICATING OILS)

lubricating value ; the latter may be determined directly by means of suitable
machines, that of Martens x being most commonly employed.

Viscometers of other types are those of Lamansky-Nobel2 (Russia), Red-
wood 3 (Great Britain) and Saybolt 4 (America). In France use is made of
Barbey's ixom&tve, which determines the coefficient of fluidity of an oil by measur-
ing the volume of an oil dropping during a certain time.

The ratio between the values of the viscosity found by the Lamansky-Nobel
and Engler apparatus respectively is about constant and is 1-13-1-18 for fluid
oils and 1-20-1-26 for more viscous oils (engine and cylinder oils), so that number
of Engler degrees = number of Lamansky-Nobel degrees divided by such factor.

The relations between Engler values and those obtained with the Red-
wood and Saybolt apparatus are given by the following formula, in which tr
and t, represent the times of efflux in the two apparatus and E the Engler degrees :

tr= IQ2-2& /i

(2)  t, = 228-7/5 (i +

(3)  k = o-oSoig-E — 0-07013



In practice, for viscosities which are not too low (not less than 3 or 4 degrees
Engler), it is a sufficiently close approximation to assume that the times of
efflux in the Engler, Redwood and Saybolt forms of apparatus (used according
to the conditions prescribed for each case) are in the ratios 100 : 59 : 70.

8. Behaviour at Low Temperature.—When strongly cooled, lubri-
cating oil first thickens and ultimately congeals and the aim of investigating
its behaviour is either to ascertain if the oil remains liquid at a certain
temperature or to discover when it begins to thicken without assuming
a tallowy consistency.

In the former case a test-tube 15 mm. in diameter is filled to a height
of about 3 cm. with the oil and placed, together with a thermometer in a
beaker about 12 cm. in height and diameter containing a salt solution of
known freezing point5 corresponding ^approximately with the temperature
at which the oil should remain liquid. The whole is placed in an earthen-
ware vessel and cooled for an hour with a freezing mixture composed of
two parts of snow or pounded ice and one part of common salt.6 The tube
is then taken from the solution to see if the oil has remained liquid.

1  D. Holde :   Untersuchung der Kohlenwasserstoffole-und Fette, Berlin, 1913, p. 158 '>
W. Hinrichsen :  Das Materialprufungswesen, Stuttgart, 1912,

2  Wischinsin and Singer :  Chem. Rev. Fette Industrie, 1897.

3  B. Redwood:  Petroleum, London, 1913.

4  B. Redwood:  Petroleum, London, 1913.

5  For this purpose the following solutions may be used :

Freezing point-                                                                       Composition.

- 10°

— 15° to — 15-4C

6  With this mixture, a temperature of — 21° may be attained.    For lower tem-
peratures, the two vessels are charged with alcohol which is cooled with solid carbon
dioxide ;  constant temperatures of — 25° and — 30° are thus obtained.

.    Water, 100
	KNO3, 13 parts.

,,           IOO
	KNOg, 13 ; NaCl, 2.

,,           IOO
	KNOg, 13 : NaCl, 3-3-

„           IOO
	BaCl2, 35-8-

„           IOO
	CaCl2, 22-5.

,,           IOO
	NH4C1, 20.

,,          IOO
	;  NH4C1, 25.

 antain more than